U.S. Sen. Ron Wyden and two colleagues on the Senate Select Committee on Intelligence are pushing the Obama administration to disclose the limits of its controversial policy on killing Americans in drone attacks.

The senior senator from Oregon, joined by fellow Democrats Mark Udall of Colorado and Martin Heinrich of New Mexico, want to learn how and when Americans can be targeted outside of declared war zones.

"Specific details regarding lethal counterterrorism actions will sometimes need to be kept secret to ensure that the U.S. government can act effectively against very real threats to our country, but we firmly believe that the laws and rules that govern the executive branch's actions should always be public," they wrote on Thursday. "We believe that every American has the right to know when their government believes it is allowed to kill them."

In their two-page letter to White House Counsel Neil Eggleston, the senators noted that they reviewed the opinions of Justice Department lawyers on the targeting of Americans during overseas counterterrorism operations.

They said they had no quarrel with the targeted killing of Anwar al-Awlaki, an American slain in a September 2011 drone attack in Yemen. Al-Awlaki, an al Qaida recruiter, was suspected of helping to plot the failed Christmas Day 2009 airline bombing by would-be martyr Umar Farouk Abdulmutallab, known as the Underwear Bomber.

The drone attack that killed al-Awlaki also killed Samir Khan, who edited al-Qaida's English speaking propaganda magazine. Khan, who also lived much of his life in the U.S., had served as an inspiration for Mohamed Mohamud, a Somali-American convicted last year of attempting to detonate a massive fertilizer bomb at Portland's Pioneer Courthouse Square in late 2010.

Mohamud wrote articles for Khan's "Jihad Recollections" magazine, and the two traded dozens of emails, according to trial testimony in Portland's U.S. District Court.

"To be clear," the senators wrote, "we believe that under the circumstances that existed at the time, the decision to use lethal force against (al-Awlaki) was a legitimate use of the president's authorities. But we also believe that the limits and boundaries of the president's power to authorize the deliberate killing of Americans need to be laid out publicly with much great specificity."

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